Aircraft fuel supply system having a dual stream tow-phase fluid pump

ABSTRACT

An aircraft fuel supply system has a two-stage fuel pump having a first centrifugal booster stage receiving a main inlet flow stream and a second positive displacement pumping stage and is combined with an eductor pump for evacuating liquid and vapor from high points in the fuel system and for compressing the fluid acted upon to a volume capable of being digested. A flow impeller means constituting a third pump receives the eductor pump discharge completely independently of the main inlet flow stream and directs the fuel acted upon back into the main stream ahead of the positive displacement stage, thereby to prevent vapor lock of the positive displacement stage.

United States Patent Cooper 1 July 15, 1975 [54] AIRCRAFT FUEL SUPPLY SYSTEM 3,551,073 12/1970 Petrovits 417/76 HAVING A DUAL STREAM TQKALPHASE 3,736,072 2/1973 $urne1' 6t 21]. 417/87 FLUID PUMP ,8l0 7l4 /l974 urner 417/80 [75] Inventor: Paul Cooper, Cleveland Heights, P i E j william L, Freeh Ohio Assistant ExaminerGregory P. LaPointe [73] Assigneez TRW Inc Cleveland Ohio Attorney, Agent, or Fzr mHill, Gross, Simpson, Van

Santen, Steadman, Chiara & Simpson [22] Filed: Jan. 30, 1974 21 Appl. No.: 437,899 [571 ABSTRACT An aircraft fuel supply system has a two-stage fuel pump having a first centrifugal booster stage receiving [2%] il-S-il 417/F7$5ib4;;/3Z a main inlet flow Stream and a Second positive i 81 87 89 placement pumping stage and is combined with an 1 o earc 2 2 eductor pump for evacuating liquid and vapor from I high points in the fuel system and for compressing the fluid acted upon to a volume capable of being di- [56] References Clted gested. A flow impeller means constituting a third UNITED STATES PATENTS pump receives the eductor pump discharge completely 2,466,792 4/1949 Conery 417/81 independently of the main inlet flow stream and di- ,5 12/1950 c g y 417/81 rects the fuel acted upon back into the main stream 2345-028 7/1958 Nash a] v r 417/31 ahead of the positive displacement stage, thereby to 1160106 12/1964 Ask/worth 415/109 prevent vapor lock of the positive displacement stage. 3,387,644 6/1968 Hemecke et all... 417/87 3,532,441 10/1970 Schofield 417/203 5 Claims, 2 Drawing Figures MAIN FLOW Ill/LE7 AIRCRAFT FUEL SUPPLY SYSTEM HAVING A DUAL STREAM TOW-PHASE FLUID PUMP BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to aircraft fuel supply systems and more particularly to an air and fuel vapor removal and regeneration system operating in conjunction with the fuel feed systems of aircraft jet engines.

2. The Prior Art The prior art is exemplified by US. Pat. Nos. 3,387,644 and 3,532,441. Thus, it has been known heretofore to collect fuel vapor and air by means of an eductor, thereby to form a fine bubble emulsion which can be safely returned into the main fuel stream. Prior art artisans have claimed advantages in returning such fluid to a specific location in the conventional twostage fuel pump, for example, at an intermediate stage of the two-stage fuel pump.

SUMMARY OF THE PRESENT INVENTION In accordance with the principles of the present invention, a flow impeller means is provided as a third pump and means form a hydraulic circuit between the eductor pump and the flow impeller means for directing the discharge of the eductor pump to the inlet of the flow impeller means independently of the main inlet flow stream. The flow impeller means are capable of digesting fluid having a volume ratio of vapor-to-liquid of 0.45 or less. Thus, the fluid acted upon may be safely directed back into the main fuel stream ahead of the positive displacement stage but after the centrifugal booster stage, thereby to prevent vapor lock of the positive displacement stage.

In one form of the invention, the flow impeller means constitutes radial impellers driven by a hub and disk common to the first centrifugal booster stage. In another form of the invention a completely separate centrifugal impeller is provided independent of the first centrifugal booster stage and such separate impeller has its own separate pumping chamber.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plumbing diagram illustrating the features of an aircraft fuel supply system incorporating the principles of the present invention wherein a completely separate centrifugal pump is used to digest air and vapor acted upon by the eductor.

FIG. 2 is a cross-sectional view of an alternative pumping arrangement wherein the flow impeller means constitute radial impellers driven by a hub and a disk common to the first centrifugal boost stage of the aircraft fuel pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As is customary in aircraft fuel pumping systems, dual stage fuel pumps are frequently used which customarily include a first centrifugal booster stage and a second positive displacement pumping stage. The present invention is intended for utilization with such an aircraft fuel pumping system. Thus, there is shown in FIG. 1 a conventional source of fuel in an aircraft such as a fuel tank designated by legend and a line leads from the fuel tank to the inlet 11 of a centrifugal first stage 12 of a fuel pump which also includes a second positive displacement stage shown at 13. It will be understood that the pressurized fluid acted upon by the dual stage fuel pump will be directed through a discharge line 14 to a fuel control unit shown diagrammatically at 16, the details of which are not necessary to the understanding of the principles of the present invention.

In contemporary aircraft, long fuel supply lines and differences in elevations of various engines on a single aircraft produce unusual conditions in the fuel lines. Thus, there is indicated diagrammatically in FIG. 1 a high point in the fuel line 10 which is designated at 17 and a line 18 leads to the venturi throat 19 of an eductor pump shown generally at 20. It will be understood that the eductor pump 20 may be powered by fluid obtained from any pressurized source, for example, excess fluid from the flow control unit 16 may be utilized, or a portion of the driving fluid can also be obtained from an interstage point between the centrifugal stage 12 and the positive displacement stage 13 of the fuel pump. In any event, the eductor pump 20 is used to draw air and vapor from the high point 17. Upon sucking off such gas, the eductor pump operates to compress it to a volume capable of being digested as a two phase mixture. In accordance with the principles of the present invention, a completely separate centrifugal flow impeller means is shown at 21 and a hydraulic circuit means 22 is provided which connects the discharge 23 of the eductor pump 20 to a inlet 24 of the flow impeller means 21. In the form of the invention shown in FIG. 1, the flow impeller means 21 has means forming its own pumping chamber 26 and a line 27 connects the pumping chamber 26 to the main fuel stream so that the two-phase fluid acted upon by the flow impeller means 21 can be discharged back into the main fuel stream. As shown in FIG. 1, the line 27 is connected as at 28 to a point after the first centrifugal pumping stage 12, but before the positive displacement pumping stage 13.

There is thus provided for an aircraft fuel system a pump capable of receiving two fluid streams, each stream being single or twophase, the predominant phase being liquid and the other phase being air and/or vapor of the specific liquid being pumped. The first or mainstream is received at a pressure P and the second or supplementary stream is at a pressure P where P P Both of the impellers of the centrifugal booster stage 12 and the flow impeller means 21 are capable of digesting fluid having a volume ratio of vapor-to-liquid V/L of 0.45 or less, and such impellers discharge pressurized liquid at a pressure P the gaseous phase having been dissolved in the liquid.

In the arrangement of FIG. 1, when the eductor 20 sucks off gas and fluid and compresses it to a volume capable of being digested by the pump, the resulting two-phase mixture is then delivered to the supplementary stream inlet port 24 at a pressure P and the main stream proceeds to its inlet port 11 at a pressure P P being therefore greater than P An amount of liquid equal to that flowing in the main steam is discharged at pressure P to the high pressure gear pump or positive displacement pump 13 which is therefore prevented from vapor locking.

Referring now to FIG. 2, another form of the invention is shown wherein the flow impeller means constitutes radial impellers driven by a hub and a disk common to the first centrifugal booster stage. In this form of the invention, the main steam inlet port is shown at 11a and the centrifugal booster impeller is shown generally at 12a and has pumping passages 121 which receive the fluid at a center inlet and discharge the fluid radially outwardly into a toroidal pumping cavity 122. The centrifugal booster stage impeller 12a has a hub formed by a shaft 123 on which is carried an outwardly extending hub flange 124, the hub flange 124 having an axial flange 126 circumjacent the hub shaft 133. On the forward side of the hub flange 124, there are provided a plurality of pumping blades 127, thereby forming pumping passages through which the fluid is directed into the toroidal pumping chamber 122.

The pump of FIG. 2 has a mounting pad 128 on which is carried the eductor 20a. The mounting pad 128 is particularly characterized by a supplementary steam inlet port 240 arranged to be in register with a port 130 formed in the eductor 20a and receiving through a passage 131 the gas and fluid acted upon by the eductor.

The inlet port 24a is directed to a center lnlet 24b and the flow impeller means, shown generally at 21a, constitutes a plurality of radial impellers 21b which are fastened to the rear side of the hub flange 124 and which operate to deliver the two-phase mixture received from the eductor 20a into the toroidal pumping chamber 122.

The hub flange 124 is locked in place on the hub shaft 133 by a bushing 140 which in turn carries a bearing member 141. A drive shaft is keyed as at 142 to the hub shaft 133, which drive shaft is shown at 143. The second stage positive displacement pump constitutes a gear pump and is shown generally at 113.

As shown in FIG. 2, the eductor 20a may be powered at least in part with fluid pressurized by the centrifugal booster impeller 121. In this regard, there is provided an inlet chamber 150 receiving fluid from the pumping chamber 122 via a passage 151. The fluid is directed through a nozzle 152. There is provided a port 153 which may be connected to receive gaseous fluid from one or a plurality of high points in the fuel system of the type exemplified by 17 (FIG. 1) and such fluid is sucked through a sleeve 154 into a chamber 156 whereupon it is directed through a venturi passage 157. It will be noted that the nozzle 152 is aligned with the venturi passage 157 and directs a jet of fluid across the space 156 into the venturi passage 157 to accomplish the the eductor action. The two-phase eductor discharge is shown moving in the directions shown by the arrows to the center inlet 24b associated with the flow impeller means 21a.

While other modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent war-- ranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention: 1. An aircraft fuel supply system comprising, a two-stage fuel pump having a first centrifugal booster stage receiving a main inlet flow stream from a source of fuel and initially pressurizing said main inlet flow stream, said fuel pumping having a second positive displacement pumping stage receiving the initiallized pressurized flow stream and pressurizing said stream for delivery to a fuel flow control unit,

an eductor pump for evacuating liquid and vapor from high points in the fuel system and for compressing it to a volume capable of being digested,

a flow impeller means constituting a third pump,

and means forming a hydraulic circuit extending between an outlet of said eductor pump and an inlet of said flow impeller means for directing the discharge of said eductor pump to the inlet of said flow impeller means independently of said main inlet flow stream, and further including means for directing the fuel acted upon by said flow impeller means into the main stream ahead of the positive displacement stage, but after the centrifugal booster stage of the fuel pump thereby to prevent vapor lock of the positive displacement stage.

2. An aircraft fuel supply system as defined in claim 1 and further characterized by said flow impeller means constituting radial impellers driven by a hub and a disk common to said first centrifugal booster stage.

3. An aircraft fuel supply system as defined in claim 1 and further characterized by said flow impeller means constituting a centrifugal impeller separate and independent of said first centrifugal booster stage and having its own inlet and outlet.

and means forming a separate pumping chamber for said flow impeller means,

whereby said means forming a hydraulic circuit are connected between said eductor pump and said inlet and between said separate pumping chamber and the main flow stream.

4. An aircraft fluid fuel pumpingsystem having an integrated air-fluid-vapor lock preventive means comprising:

1. a two-stage pumping means having a first stage comprised of a first centrifugal boost pump discharging to a second stage comprised of a positive displacement gear pump and being operable in such a manner that the output of said first stage is greater than the input capacity of said second stage, I t

a selected number of high point air-fuel-vapor accumulation chambers located along the length of the main fuel flow path in the fuel pumping system,

an eductor pumping means connected to said high point accumulation chambers and receiving a motive flow including said excess output from said first stage thereby operable to draw said air-fuelvapor accumulations into said eductor pumping means to produce a two-phase flow,

a second centrifugal flow impeller means, and hydraulic circuit means extending between an output portion of said eductor pumping means and an inlet portion of said second centrifugal flow impeller means, whereby said two-phase flow is pressurized to a level equal to that of the output pressure of said first centrifugal boost pump, and hydraulic circuit means for introducing the regenerated air-fuelvapor accumulations into the main fuel flow of the system ahead of said positive displacement pump and after said first centrifugal boost pump.

5. A liquid fuel pumping system with an integrated air-fuel-vapor regenerating means as defined in claim 4,

said se cond centrifugal flow impeller means being mounted on a common disk and head of said first centrifugal boost pump, and having a separate inlet receiving a two-phase fluid flow comprised of said air-fuel-vapor and the motive fluid flow discharged boost pump, and radially discharged into said toroifrom said eductor pumping means, wherein said dal output chamber of said first stage centrifugal tw-phasc fluid flow is pressurized to a level equal boost pump. to the output pressure of said first stage centrifugal 

1. An aircraft fuel supply system comprising, a two-stage fuel pump having a first centrifugal booster stage receiving a main inlet flow stream from a source of fuel and initially pressurizing said main inlet flow stream, said fuel pumping having a second positive displacement pumping stage receiving the initiallized pressurized flow stream and pressurizing said stream for delivery to a fuel flow control unit, an eductor pump for evacuating liquid and vapor from high points in the fuel system and for compressing it to a volume capable of being digested, a flow impeller means constituting a third pump, and means forming a hydraulic circuit extending between an outlet of said eductor pump and an inlet of said flow impeller means for directing the discharge of said eductor pump to the inlet of said flow impeller means independently of said main inlet flow stream, and further including means for directing the fuel acted upon by said flow impellEr means into the main stream ahead of the positive displacement stage, but after the centrifugal booster stage of the fuel pump thereby to prevent vapor lock of the positive displacement stage.
 2. An aircraft fuel supply system as defined in claim 1 and further characterized by said flow impeller means constituting radial impellers driven by a hub and a disk common to said first centrifugal booster stage.
 3. An aircraft fuel supply system as defined in claim 1 and further characterized by said flow impeller means constituting a centrifugal impeller separate and independent of said first centrifugal booster stage and having its own inlet and outlet, and means forming a separate pumping chamber for said flow impeller means, whereby said means forming a hydraulic circuit are connected between said eductor pump and said inlet and between said separate pumping chamber and the main flow stream.
 4. An aircraft fluid fuel pumping system having an integrated air-fluid-vapor lock preventive means comprising:
 5. A liquid fuel pumping system with an integrated air-fuel-vapor regenerating means as defined in claim 4, said second centrifugal flow impeller means being mounted on a common disk and head of said first centrifugal boost pump, and having a separate inlet receiving a two-phase fluid flow comprised of said air-fuel-vapor and the motive fluid flow discharged from said eductor pumping means, wherein said two-phase fluid flow is pressurized to a level equal to the output pressure of said first stage centrifugal boost pump, and radially discharged into said toroidal output chamber of said first stage centrifugal boost pump. 